(1) Field of the Invention
This invention relates to an apparatus having a color monitor for determining color separation conditions and a method for correcting the color signals and a masking circuit therefor.
When color pictures are printed by using color originals such as color photographs, color separation films are prepared by separating the colors of the original by means of a color separation device such as a color scanner.
The present invention relates to an apparatus for determining the color separation conditions. A color original is first scanned to obtain electrical signals representing the image, the image signals are corrected so as to be printed desirably, and in order to make the image on a color monitor practically exactly the same as the image that will be actually printed, the corrected image signals are further corrected. By developing the twice-corrected image signals on the color monitor, the conditions for the color separation process can be accurately determined. The present invention further relates to the method for the above color signal correction and to the masking circuit which is used in the above apparatus.
(2) Description of Prior Art
Printing a color original such as a color photograph comprises the following three steps in general. The first step is color separation, in which color separation films are prepared by separating the colors of the original picture by means of a color separation device such as a color scanner. The second step is preparing the printing plates from the color separation films. In the third step the printing plates are attached to a printing press and the printed matter is produced.
In this process, a fully-colored image is obtained only in the final actual printing step, and it is therefore quite difficult to ensure that the final printings will have good colors.
For example, in the case that the tone of color is not desirable in the original picture, each color is conventionally corrected in the intermediate steps (mainly in the color separation step), but, it is difficult to judge whether the correction made is adequate or not until the final printed matter is produced.
To remedy this problem, so-called previewing apparatus has been proposed recently, in which apparatus an image that accurately represents the image that will actually be printed is developed on a color television screen so as to check up the colors of image in each step.
Such apparatus is exemplified by the previewing apparatus of Hazeltine Research, Inc. as disclosed in U.S. Pat. No. 3,131,252, and the apparatus of the present applicants, which is disclosed in U.S. Pat. No. 3,972,066. Apparatus for determining the conditions in color separation step by previewing, is exemplified by an apparatus of Dr.-Ing. Rudolf Hell GmbH disclosed in West German Offenlegungsschrift No. 2,607,623. In the apparatus of Hell GmbH, a previewing device and a color scanning device are combined in series.
In the previewing apparatus of this kind, the most inportant matter is how the image on the color television monitor is to be made an accurate representation of the actually printed image. In addition, when apparatus of this kind is used, it is regulated according to various conditions (by regulating correction factors), and the second important matter is that such regulation be easily carried out.
Many of the conventional apparatuses mentioned above have suffered from inaccurate color reproduction, as well as, in one case, the inconvenience of the method of regulation of the apparatus.